1. Field of the Invention
The present invention relates generally to electrical penetrator assemblies for feed through of electrical power through the wall of a pressurized vessel or the like, and is particularly concerned with hermetic sealing of exposed end portions of an electrical penetrator assembly for use in subsea or other harsh environments.
2. Related Art
Electrical penetrators are used to power subsea electric submersible pump (ESP) equipment and the like which pump hydrocarbons in oil well installations, and also in other applications such as high pressure downhole electrical penetrations and other penetrations to provide power to various types of subsea equipment. The penetrator extends through the wall or bulkhead of the vessel in which the equipment is located, and is normally connected to power cables at one end for connecting the equipment to an external power source. In an ESP application, the connection or penetrator cannot be isolated from the pumping pressure for practical reasons. This creates an extreme environment for the connector or penetrator in terms of pressure, temperature, and high voltage. The penetrator must transfer power to the motor as well as maintaining a pressure barrier for both internal pressure created by the ESP and external pressure caused by the depth in seawater. The temperatures are increased due to fluid temperatures as well as resistive heating of the electrical elements.
In a typical electrical penetrator or feed through arrangement, a one-piece conductor such as a conductive connector pin extends through a bore in an insulating sleeve or body, with appropriate seals brazed or bonded between the outer body and pin at each end of the penetrator assembly. The penetrator extends through a bore in an outer connector body or shell. In some cases, multiple penetrators extend through the outer shell. One end of the penetrator is exposed to a relatively high pressure environment inside a subsea housing, and a second end is exposed to ambient pressure of the subsea environment. In one known arrangement, the seals comprise metal sealing sleeves which seal the insulating sleeve of ceramic or the like to the conductive connector pin body. Due to the heat involved during the brazing or bonding process, the parts expand by different amounts. Once the penetrator assembly is allowed to cool, the different rates of shrinkage of the different material parts causes stress on the ceramic housing material, brittle bonds, or both, and may lead to failure of the seal. Thus, known penetrator sealing or encapsulation methods involving surface plating or coating may not stand up to the wear and abrasion that can occur in handling, assembly, and repeated subsea mate/de-mate processes, and corrosion may occur at the brazed or welded interfaces.